The present disclosure concerns apparatus for securing a blade in a gas turbine and particularly a lock plate that inhibits axial movement of a blade relative to the hub.
FIG. 1 depicts an high pressure compressor disc 2 of a gas turbine engine. The disc 2 has a plurality of axial slots 4 extending into the disc from its circumferentially outer surface 6 with the slots being arranged in an array that extends around the circumference of the disc. Each slot is shaped to receive a blade root with the shape of the slot and the corresponding shape of the root being designed to hold the blade within the disc despite the centripetal forces on the blade as the disc rotates in use. The slot may be formed as a dovetail 8, a fir tree, or other suitable shape.
To inhibit axial movement of the blade in the slot 4 in use one or more lock plates are provided. These plates are located partly within a circumferential slot 10 that is defined in part by an overhang 12 in the disc hub and in part by an overhang 14 in the blade 16. Each overhang is provided by a forward extension projected from the hub or blade root and which has a radially inwardly extending portion at its distal end.
The plates are inserted within the slot to engage the fixed overhangs on the disc and the translatable overhangs on the blade to inhibit the axial movement of the blade relative to the disc. A lock plate or lock plates are provided to secure prevent the plates from becoming detached from the slot. In one known example of a lock plate the plate is formed out of a planar sheet that is bent out of plane to provide a curved cross-section. The curvature is sufficient to shorten the width of the lock plate so that it can be inserted within the slot after which it is straightened e.g. by applying a force—impact or continuous—to lock the plate within the slot.
At overhaul the lock plate is destructively removed e.g. by cutting or levering the lock plate from the slot to release the blades from the disc. By this method of removal there is a reasonable risk of loss of the lock plate that would have to be re-found before the engine could be put back into service, or damage to the disc that may subsequently need to be scrapped.